The utilization of flat panel display devices is popular and widespread. The flat panel display devices are usually employed in flat panel TVs, mobile phones, PDAs, digital cameras, display panels in automobiles, and projectors.
Referring to FIG. 1, it is a diagram illustrating a flat panel display device structure in prior art, comprising a thin film transistor (TFT) 11; a light generation device 12 wherein one terminal of the light generation device 12 couples with a drain 112 of TFT 11; and a modulation unit 13 wherein an output couples with a gate 111 of TFT 11. Users can change an input signal 131 of the modulation unit 13 to modify an output signal 132 based on a signal transformation curve. The TFT 11 outputs current into the light generation device 12 from the drain 112 in accordance with the input signal of the gate 111 and the threshold voltage between the gate 111 and the drain 112. The light intensity of the light generation device 12 increases as the input current of the light generation device 12 raises.
Referring to FIG. 2, it is a graph illustrating the signal transformation curve in a coordinate, wherein the horizontal axis represents the input signal 131 which can be a digital signal and the vertical axis represents the mentioned output signal 132 which can be an analog voltage output. The signal transformation curve 21 representing the corresponding relationship between the input signal 131 and the output signal 132 is similar to a Gamma curve. Users input the input signal 131 in the modulation unit 13 to produce a corresponding output signal 132.
Referring to FIG. 3, it is a modulation unit known as a prior art, comprising two adjustable resistors 31, 32 and resistors in serial 33 wherein the resistors in serial 33 comprises a plurality of resistors in serial and a plurality of voltage bias points 34. One terminal of the adjustable resistor 31 is connected to a highest input voltage 35 with a highest voltage point 36. One terminal of the other adjustable resistor 32 is connected to a lowest input voltage 37 with a lowest voltage point 38. The modulation unit provides a highest voltage output as the same as the voltage value of the highest voltage point 36 and a lowest voltage output as the same as the voltage value of the lowest voltage point 38. The voltage values of the voltage bias points 34 are limited between the highest voltage and the lowest voltage outputted by the modulation unit. It is known as a prior art that there are provided n voltage bias values in a modulation unit where n is a number of 2 to the power of n, i.e. 2^n, and the n-th voltage bias value can be outputted according to the digital input, i.e. n th voltage bias, from users. The relationship between the digital inputs and analog outputs are described in the signal transformation curve in FIG. 2. In a word, users can change the voltage bias value of the voltage bias points 34 by modifying the resistance values of the adjustable resistors 31, 32.
Referring to FIG. 4, it is a graph illustrating the signal transformation curve in a coordinate with the modulation unit described to FIG. 3 wherein the horizontal axis represents an input signal 41 and the vertical axis represents an output signal 42. The signal transformation curve 43 represents the corresponding relationship between input signals 41 and output signals 42. While decreasing the resistance value of the adjustable resistor 33, the left part of the signal transformation curve 43 moves toward the direction A. While increasing the resistance value of the adjustable resistor 33, the left part of the signal transformation curve 43 moves toward the direction B. It is similar that while decreasing the resistance value of the adjustable resistor 34, the right part of the signal transformation curve 43 moves toward the direction C. While increasing the resistance value of the adjustable resistor 34, the right part of the signal transformation curve 43 moves toward the direction D. Thus, the curvature and linearity of the signal transformation curve 43 can be changed, i.e. the relationship between input signals 41 and output signals 42, by tuning the resistance values of the adjustable resistors 33, 34. When the characteristics of the TFT coupling with the modulation unit are fine tuned so as to have a proper signal transformation curve 43, the light generation device coupling with the TFT obtains an expectable current value and an appropriate light intensity.
Although the modulation units mentioned above can tune the signal transformation curve, the range of modification of the signal transformation curve is restricted by adjusting the adjustable resistors. In fact, during the manufacturing process of the flat panel display devices, the drafting effect makes the threshold voltages of each TFT on the flat panel display devices different. The light intensity of the light generation devices is not acceptable due to the inputting current of the light generation devices is not exact the same, even all of the inputting voltages on the gates of the TFT transistors are precisely the same. The difference of the threshold voltage between TFT transistors is created by the conditions of manufacturing environment in reality. The difference can be about 1 voltage and causes the display quality of the flat panel display devices and light intensity of the display devices are undesirable.
It is an objective of the present invention to provide a flat panel display device structure including a modulation unit for adequately shifting vertically the signal transformation curve to solve the restricted shifting of the signal transformation curve in prior art. Another flat panel display device structure containing a modulation unit is disclosed, too.